Vacuum pumps

ABSTRACT

A vacuum pump, particularly for automotive use, comprises a stator ( 2 ) and a rotor ( 24 ) mounted to be rotatable about an axis. The rotor ( 24 ) is connected to a first circular section annular member ( 18 ) coaxial with the axis, the outer surface of which constitutes the bearing surface of a pulley or gearwhell, in particular a multi-V pulley. The first circular section annular member ( 18 ) defines a space in which the rotor and stator are accommodated.

The present invention relates to vacuum pumps, particularly for automotive use, that is to say vacuum pumps for use on motor vehicles.

An increasing proportion of motor vehicles have a requirement for a vacuum source, e.g. to operate servo systems or the like and it is, therefore, increasingly common for motor vehicles to include a vacuum pump. Such pumps are accommodated in the engine compartment of the vehicle and are driven by a belt and pulley arrangement connected to be driven directly or, more usually, indirectly by the crankshaft. As automotive engines become progressively more sophisticated, the engine space of such vehicles becomes ever more crowded. Automotive designers are therefore constantly seeking innovative ways of packaging the numerous components and devices which are accommodated in the engine compartment so as to minimise their space requirement.

It is, therefore, the object of the invention to provide a vacuum pump of the type which has a minimal additional space requirement and can thus be fitted into a very confined space, such as a vehicle whose engine compartment is already nominally full.

In accordance with the present invention, a vacuum pump comprises a stator and a rotor mounted to be rotatable about an axis, the rotor being connected to a first circular section annular member coaxial with the axis, the outer surface of which constitutes the bearing surface of a pulley or gearwheel, the first circular section annular member defining a space in which the rotor and stator are substantially accommodated.

The present invention is based on the recognition that modern automotive engines typically include at least two pulley wheels, one of which is typically connected to the crankshaft and around which a pulley passes. The other pulley wheel or pulley wheels are connected to auxiliary devices, such as an alternator, a power steering pump, an air conditioning pump or the like and are driven by means of a pulley belt which passes around them and the crankshaft pulley. Such pulley belts were traditionally of simple V type and thus had a relatively small length in the axial direction, that is to say parallel to the axis about which they are mounted to rotate. However, V pulley belts have a tendency to slip and ultimately to break and they are increasingly being replaced by so-called multi-V pulley belts, which comprise a relatively wide belt, the outer surface of which is flat and the inner surface of which affords a plurality of V section projections. Such pulleys pass over multi-V pulley wheels, whose outer surface affords a plurality of V shaped recesses which accommodate the V shaped projections on the belt. Whilst such multi-V pulley belts are very much more reliable and have a substantially reduced tendency to slippage and breakage, they do take up considerably more space than traditional single V pulley belts. Multi-V pulley wheels also take up considerably more space than single V pulley wheels and typically have a length in the axial direction of 3 cm or even more. The space within such pulley wheels is traditionally “dead space” and remains unused. However, the vacuum pump in accordance with the invention is accommodated within the space within a pulley and thus has effectively a zero additional space requirement. This pulley is likely to be of multi-V type but it could also be of single-V type or flat belt type or a chain drive pulley. Indeed, instead of a pulley a gearwheel, such as a sprocket might be used. The vacuum pump in accordance with the invention is therefore effectively an integrated unit comprising a vacuum pump and either a pulley wheel or a gearwheel.

Vacuum pumps generally include a rotor mounted within a stator. The stator constitutes the external casing of the pump or is connected to a further enclosure which constitutes the outer casing. In all cases, the outer casing of the pump is stationary and the moving component, that is to say the rotor, is safely accommodated within it. However, in the integrated vacuum pump and pulley wheel of the present invention, the outer casing, which is effectively the pulley wheel, is connected not to the stator but to the rotor and therefore rotates, in use. This would normally be considered to be unacceptable for safety reasons but when used in the form of an integrated vacuum pump and pulley wheel it constitutes no additional safety risk because pulley wheels in any event inherently rotate and automotive pulley wheels are in any event generally shielded from inadvertent access by virtue of their accommodation in the engine compartment of a vehicle.

It is preferred that the rotor is afforded by a first end plate assembly comprising a first plate extending in a radial plane and connected to one end of the rotor and to the first annular member. The rotor, first annular member and first plate thus constitute a unit, which might be referred to as a rotor end plate assembly and effectively constitutes a pulley wheel which differs from the conventional pulley wheel only in its internal construction.

The vacuum pump may be of various known kinds but it is preferred that it is of eccentric rotor sliding vane type. The stator is preferably afforded by a second end plate assembly comprising a second plate which extends in a radial plane and through which extend a rotary shaft connected to the rotor and inlet and outlet openings and connected to the outer edge of which is a second circular section annular member, which fits within the first annular member.

In one embodiment, the stator comprises an eccentric circular space, which is defined within the second end plate assembly and rotatably accommodates the rotor, the rotor carrying the sliding vanes. The pump is therefore of conventional eccentric rotor sliding vane type in which the rotor rotates within the stator and carries a number of vanes which are slidably accommodated in outwardly extending slots. These vanes form a sliding seal with the two end plates and are forced by centrifugal force into sliding contact with the inner surface of the stator.

However, in an alternative embodiment, the rotor comprises an eccentric circular space, which is defined within the first plate assembly and accommodates the stator, the stator carrying the sliding vanes. In this embodiment, it is the eccentric circular space that rotates and it is the stator that accommodates the sliding vanes. These vanes are again in sliding contact with the two end plates but no centrifugal force acts on them to press them into sliding contact with the internal surface of the rotor. This contact must therefore be produced by some other means, e.g. by the provision of one or more compression springs at the base of each slot which urges the associated vane outwardly.

Thus, in use, the stator end plate assembly is anchored to a fixed structure on the vehicle and a rotary shaft passes through it, one end of which is connected to the rotor and the other end of which may be connected e.g. to an auxiliary device, such as an air conditioning fan. The integrated vacuum pump and pulley wheel may thus constitute the pulley wheel connected to an auxiliary device for the purpose of driving it by means of a multi-V belt which passes around both it and a further driven pulley wheel, e.g. connected to the engine crankshaft.

Further features and details of the invention will be apparent from the following description of one specific embodiment which is given by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view from one end of an integrated vacuum pump and pulley wheel in accordance with the invention;

FIG. 2 is a perspective view similar to FIG. 1, but from the other end; and

FIG. 3 is an exploded side view of a second embodiment comprising an integrated pump and gearwheel.

The pump shown in FIGS. 1 and 2 consists essentially of a stator end plate assembly 2 and a rotor end plate assembly 4. The stator end plate assembly 2 comprises an annular band or strip 3 of circular shape, integral with one end of which is a circular end plate 6. Formed in the centre of the plate 6 is an aperture 8, accommodated within which is a bearing bush 10. Also formed in the plate 6 is a small inlet hole 12 and a rather larger outlet hole 14. Situated within the space defined by the plate 6 and annular member 3 is an upstanding wall 16 which constitutes the stator of the vacuum pump and defines a circular section space, the axis of which is eccentric, that is to say offset from the axis of the opening 8.

The rotor end plate assembly comprises an annular member or band 18 of circular section, the axis of which is coaxial with the axis of the hole 8 in the plate 6. Integral with one end of the annular member 18 is a circular end plate 20. The outer surface of the annular member 18 carries a plurality of V-shaped projections 22 and constitutes a multi-V pulley. Situated within the space defined by the annular member 18 and the end plate 20 is a circular section formation 24, the axis of which is coaxial with the axis of the hole 8. The formation 24 constitutes the rotor of the vacuum pump. Axially connected to the rotor 24 is a rotary shaft 26 which extends through and is located by the bearing bush 10 in the hole 8.

Formed in the stator 24 are four slots 26, each of which is located in a respective plane which extends generally in the outward direction and in a direction parallel to the axis of the shaft 26. Accommodated in each slot 26 is a respective sliding vane 28, each of which constitutes a rectangular plate of self-lubricating material, e.g. a phenolic-cotton fabric laminate material incorporating molybdenum disulphide, such as that designated NP313, NP322, NP344 or NP347 and sold by Norplex, Inc. of Iowa, U.S.A.

When the two end plate assemblies are connected together, the stator end plate assembly is essentially received within the rotor end plate assembly and the rotor 24 is received within the stator 16. Both of these are of circular section but their axes are offset and a gap is therefore defined between them of crescent shape, which constitutes the working space of the pump. The inlet hole 12 communicates with one end of the working space and the outlet hole 14 communicates with the other end.

In use, the composite vacuum pump and pulley wheel constitutes the drive pulley on e.g. a vehicle water pump. A multi-V pulley belt passes round a multi-V pulley carried on the crankshaft and around the composite vacuum pump and pulley wheel of the present invention and optionally also round one or more further pulley wheels in order to drive the auxiliary devices to which those pulley wheels are connected. The stator end plate unit is connected to some fixed structure in the engine, e.g. the water pump housing. When the engine is operated, the pulley wheel is rotated by the pulley belt and the rotor rotates rapidly within the stator. The vanes are flung outwardly by centrifugal force and form a seal with the internal surface of the annular member 18 and the two end plates 6 and 20. Defined between each adjacent pair of vanes is a cell, that is to say a working space, which rotates around the axis of the shaft 26. The volume of each cell progressively increases and then decreases again. The inlet hole communicates with the cells at a position at which their volume is increasing and the outlet hole 14 communicates with the cells at a position at which their volume approaches zero. A reduced pressure or vacuum is therefore produced in the inlet hole 12 and this is connected by appropriate pipe work to a vacuum reservoir for use, as required, e.g. for operating servo systems on the vehicle.

The composite vacuum pump and pulley wheel occupies precisely the same amount of space as would have been occupied if the pulley wheel were of non-composite type. This means that the additional space requirement of the vacuum pump is effectively zero.

FIG. 3 shows a modified embodiment in which a vacuum pump is integrated in an automotive gearwheel. This embodiment is the same as the preceding embodiment in all respects save one, namely that the external surface of the annular member 18 is configured in the form of a gearwheel and thus carries gear teeth on its external periphery. 

1. An automotive vacuum pump comprising a stationary stator and a rotor mounted to be rotatable about an axis with respect to the stator, the rotor being accommodated within the stator and connected to a first circular section annular member coaxial with the axis, the outer surface of which constitutes the bearing surface of a pulley or gearwheel, the first circular section annular member defining a space in which the rotor and stator are substantially accommodated.
 2. A pump as claimed in claim 1 in which the rotor is afforded by a first end plate assembly comprising a first plate extending in a radial plane and connected to one end of the rotor and to the first annular member.
 3. A pump as claimed in claim 1 in which the stator is afforded by a second end plate assembly comprising a second plate which extends in a radial plane and through which extend a rotary shaft connected to the rotor and inlet and outlet openings and connected to the outer edge of which is a second circular section annular member, which fits within the first annular member.
 4. A pump as claimed in claim 1 which is of eccentric rotor sliding vane type.
 5. A pump as claimed in claim 4 in which the stator comprises an eccentric circular space, which is defined within the second end plate assembly and rotatably accommodates the rotor, the rotor carrying the sliding vanes.
 6. A pump as claimed in claim 4 in which the rotor comprises an eccentric circular space, which is defined within the first plate assembly and accommodates the stator, the stator carrying the sliding vanes.
 7. A pump as claimed in claim 1 in which the outer surface of the first circular section annular member constitutes the bearing surface of a multi-V pulley. 